In recent years, in the production of semiconductor elements and liquid crystal display elements, advances in lithography techniques have lead to rapid progress in the field of pattern miniaturization. Typically, these miniaturization techniques involve shortening the wavelength of the exposure light source. Conventionally, ultraviolet radiation such as g-line and i-line radiation has been used, but nowadays, KrF excimer lasers (248 nm) have been introduced.
Furthermore, one example of a resist material that satisfies the high resolution conditions required to enable reproduction of a pattern of minute dimensions is a chemically amplified resist composition, which includes a base resin that exhibits changed alkali solubility under the action of acid, and an acid generator that generates acid upon exposure. Chemically amplified resist compositions include negative compositions, which contain a cross-linking agent and an alkali-soluble resin that acts as a base resin, and positive compositions, which contain a resin that exhibits increased alkali solubility under the action of acid.
Recently, the miniaturization of semiconductor elements has progressed even further, and the development of processes that use ArF excimer lasers (193 nm) is being vigorously pursued, and as a result, a variety of chemically amplified resist compositions have been developed for use with KrF excimer lasers and for use with ArF excimer lasers.
Examples of acid generators that have been used in these types of chemically amplified resist compositions are numerous, and include onium salt-based acid generators such as iodonium salts and sulfonium salts, oxime sulfonate-based acid generators, diazomethane-based acid generators such as bisalkyl or bisaryl sulfonyl diazomethanes, poly(bis-sulfonyl)diazomethanes and nitrobenzyl sulfonates, iminosulfonate-based acid generators, and disulfone-based acid generators.
In resist compositions for use with ArF excimer lasers, the so-called onium salt-based acid generators, which exhibit a powerful acid-generating capability, are the most widely used (for example, see patent reference 1).
[Patent Reference 1]
Japanese Unexamined Patent Application, First Publication No. Hei 7-234511